Method for manufacturing needles for fibrillating rollers

ABSTRACT

A method and apparatus for the manufacture of metal needles, having torpedo-shaped or bullet-shaped points, for the use in fibrillating rollers. A metal wire is passed through a first pair of driven rollers and into a second pair of rollers driven at a greater speed. The two pairs of rollers are connected in an electrical circuit. Upon entering into the second pair of rollers, the wire closes the circuit, is electrically heated and mechanically tensioned and breaks. The circuit comprises a timedelay relay, the extent of the time-delay being determinative for the shape of the needle points.

0 United States Patent 1 I 1 3,772,495

Klaase Nov. 13, 1973 [54] METHOD FOR MANUFACTURING 3,401,723 9/1968 Petry 219/68 X NEEDLES FOR FIBRILLATING ROLLERS 3,431,384 3/1969 Cooper 219/68 [75] Inventor: Petrus Theodorus Antonius Klaase,

voorburg, Netherlands Primary Examiner-R. F. Staubly [73] Assignee: Nederlandse Organisatic Voor Bl'umbaugh et Toegepost.Natuurwetenschappelijk Onderzoek Ten Behoeve Von Nl verheld, Hague, Netherlands ABSTRACT [22] Filed: Mar. 15, 1972 [211 App] No: 234,813 A method and apparatus for the manufacture of metal needles, having torpedo-shaped or bullet-shaped u points, for the use in fibrillating rollers. A metal wire [30] Forelg Apphcauon Pnomy D is passed through a first pair of driven rollers and into Mar. 19, 1971 Netherlands 7103724 a second pair of rollers driven at a greater speed. The

two pairs of rollers are connected in an electrical cir- [52] U.S. Cl. .1 219/68, 140/140 cuit. Upon entering into the second pair of rollers, the [51] Int. Cl 823p l/0 0, B2lf 21/00 wire closes the circuit, is electrically heated and me- [58] Field of Search 219/68; 140/140 chanically tensioned and breaks. The circuit comprises a time-delay relay, the extent of the time-delay [56] References Cited being determinative for the shape of the needle points.

UNITED STATES PATENTS 2,706,231 4 1955 Tyler et a]. 219/68 6 Claims, 1 Drawing Figure 2 l/; i F L j 2a Q} {i} Mi L 3 I a /2b I, v i l I /25 I L g 11 PAIENIEnnnv 13 1975 METHOD FOR MANUFACTURING NEEDLES FOR FIBRILLATING ROLLERS The invention relates to a method for manufacturing thin metal needles with at least at one end a torpedoshaped point.

Such needles are used for assembling needle rollers for the fibrillation of plastic films and must be very thin for example 50 p. m and straight, with a view to the desired rate of fineness and uniformity of the rollers. Because they, moreover, must have a great resistance to wear so as not to lose their torpedo-like pointed shape, only needles of hardened steel, molybdenum, iridium, tungsten and the like metals that are difficult to machine are eligible.

The manufacture of these needles with the aid of machining methods known in the art is cumbersome and expensive and results in a product that does not come up to the requirements to be met.

It is the object of the invention to provide a method that, with the aid of simple operations and appliances that are easily to be automated, yields needles with a v constant quality that meets the requirements.

Therefore, the method according to the invention is, characterized in that a continuous wire, whose thickness and material correspond with those of the needles to be manufactured and which is fed through a first driven pair of rollers, is brought again and again with its front end between the rollers of a second pair of rol lers, an. increasing tensile force is exerted on the part of the wire that hereafter is situated between the pairs of rollers by driving the second pair of rollers at a speed that is greater than that of the first pair of rollers, and then such an electric current is fed through the said part of the wire that this part of the wire is heated to a temperature at which it breaks off under the influence of the tensile stress. The part of the wire which is broken off forms a needle and is collected at the discharge side of the second pair of rollers. Immediately hereafter the front part of the wire is again brought between the rollers in order to form a next needle.

This method yields needles with a point on each end. It has been found that the shape of the points is mainly determined by the temperature of the wire on the location of the breakage at the moment of breaking and that there is a temperature range within which the desired torpedo shape of the point is obtained. At lower temperatures of breakage the needle point has a more or less flat end face and at higher temperatures of breakage a globular end. Needles with these shapes of the point are not usable for the designed application in fibrillating rollers.

Only fora short period of time and locally the wire has the temperature of breakage. This makes it difficult to determine at which temperature of breakage the desired pointed shape of the needle is obtained, while it is practically out of the question to reproduce that temperature again and again and under varying circumstances.

This problem is avoided, however, if the method according to the invention is further characterized in that each time after the end of the wire has been. carried into the second pair of rollers, a certain period of time is allowed to pass before the electric current is fed through the wire.

ln this method, use is made of the fact that the tensile strength of a metal wire depends on the temperature according to a fixed correlation. Each time when the wire is carried with its end into the second pair of rollers, the difference in speed between the pairs of rollers causes a tensile stress that increases as a function of the time, so that after a certain course of time there is a certain tensile stress in the wire. Then by heating the wire quickly with the aid of a sufficiently great current, it is achieved that the wire breaks at the temperature at which the tensile force of the wire is equal to the prevailing tensile stress; as the breakage of the wire interrupts the electric current, there is no further increase in temperature.

From the above it appears that the temperature at which the wire breaks can be chosen arbitrarily with the aid of the time interval with which the electric current is delayed and that in order to obtain usable needles it is sufficient to determine experimentally at the given speed of the pairs of rollers and at the given properties of the wire, at which delay time the needles have the desired pointed shape.

Preferably the wire is guided between the two pairs of rollers with the aid of a straight tube that is situated with its ends near the place of output of the first pair of rollers and the place of intake of the second pair of rollers. This guidance simplifies bringing the wire end into the second pair of rollers and at the same time offers the possibility to protect the wire against oxidation by the surrounding atmosphere. For this purpose a gas inert to the material of the wire is fed into the tube, so that the air is driven out of it and cannot affect the material of the wire.

The gas stream has a cooling effect upon the wire and has been found to be a means to influence the place where the wire is heated most quickly and the breakage finally arises. I

Of this, use is made in a preferential embodiment of the method according to the invention because .a stream of the gas is brought into the tube in a place between the ends and it is allowed to flow away to both ends. lf, moreover, in the direction of the first pair of rollers a stronger gas stream is fed through the tube than in the direction of the second pair of rollers, the result is that, approximately midway between the location of the gas supply and the second pair of rollers, the wire is heated most quickly and breaks and that the needles are very uniform in length.

The invention also relates to a device for the manufacture, according to the method described, of thin needles with at least at one end a torpedo-shaped point. This device is characterized by a drafting device of which the two pairs of rollers, which are driven at different circumferential speeds, are electrically insulated from each other and connected to the opposite poles of a sourceof current.

In order to ensure in a simple way that the wire each time breaks at the same specific temperature and yields needles with a constant pointed shape, the device according to the invention is preferably still characterized in that in the connection of one of the pairs of rollers with the source of current a time-delay relay is inserted that prevents the passage of current up to a certain interval of time after an electrical connection has been made between the pairs of rollers.

Further characteristics of the device that are related to the preferential embodiments of the device are described below with reference to the drawing in which a device according to the invention is shown partially schematically.

On baseplate 1 two parallel identical arms 2 are attached, the front one of which has partially been left out of the drawing. Between arms 2 two rollers 3 and 4 are situated. Roller 3 has its hearings in arms 2 and roller 4 has its bearings in two blocks 5, which are slidable in slots 6 of arms 2. On blocks compression springs 7 operate, which press roller 4 against roller 3 with a force adjustable by means of screws 8.

A motor 9 provided with a reduction gear drives roller 3 clockwisely at a constant speed. Roller 4 is coupled with roller 3 by means of a set of cog wheels not shown in the drawing and rotates anticlockwisely at the same speed. 1

In a corresponding way two arms 10 attached to baseplate I bear two rollers 11 and 12. Roller 11 has its bearings in arms 2 and roller 12 in two blocks 13, slidable in slots 14 and on towhich springs 15 exert a force adjustable with the aid of screws 16.

A motor 17 drives roller 11 clockwisely and roller 12 anticlockwisely at a speed greater than that of rollers 3 and 4. Consequently the device described so far forms a drafting device.

A funnel-shaped inlet pipe 18 is situated with its lower end as close as possible to the tangent of rollers 3 and 4. Between the pair of rollers 3, 4 and the pair of rollers 11, 12 guiding tube 19 is placed such that its narrowed upper end 20 is as close as possible to the tangent of rollers 3, 4 and its likewise narrowed lower end 21 as close as possible to the tangent of rollers 11, 12. Furthermore, the tube is provided with a side tube 22, which is connected to a duct (not shown) for the supply of argon or another inert gas.

Baseplate 1 is of pertinax and guiding tube 19 of glass, so that the metal assembly of bearing arms 2 with the pair of rollers 3, 4 is electrically insulated from the likewise metal assembly of bearingarms 10 with the pair of rollers ll, 12.

Via arms 2, a duct 23, an electronic relay24 and a duct 25, the pair of rollers 3, 4 is connected to the negative terminal of a direct current source 26. The pair of rollers 11, 12 is connected to the positive terminal of direct current source 26 via arms 10 and duct 27.

The operation of the device is as follows:

Metal wire 28 from which theneedles must be manufactured, is situated on a bobbin 29 above the pair of rollers 23, 4. Wire 28 is brought with its end into tube 18, caught by rollers 3 and 4 and transported by them into tube 19. As soon as wire 28 with its end emerges from lower end 21 of tube 19, it is caught by the pair of rollers 11, 12. Now, wire 28 with current source 26 and relay 24 forms a closed circuit with the result that in relay 24 a condenser 30 is charged via an adjustable resistor 31. The increasing voltage of condenser 30 is transmitted on to the control electrode of a thyristor 33 by a transistor 32 connected as an emitter-follower. This thyristor 33 initially is in a non-conducting condition but as soon as condenser 30 has been charged so far that its voltage exceeds a certain threshold value, the thyristor becomes conductive and in the circuit a current begins to pass, which quickly heats the part of the wire that is situated between the pairs of rollers 3, 4 and 11, 12.

In the meantime, after wire 28 was caught by the pair of rollers 11, 12, the part of the wire between the pairs of rollers 3, 4 and 11, 12 has been subjected to an increasing tensile stress as a result of the greater speed of rotation of rollers 11 and 12. The magnitude of this stress at the moment that this part of the wire is heated by the electric current depends on the period of time that then has passed after the end of the wire was caught by the pair of rollers ll, 12 and it is the same as the period of time that was required to charge condenser 30 up to'the threshold voltage of thyristor 33. This period of time and herewith also thestress in wire 28 at the moment of heating can be adjusted with the aid of resistor 31 The increase in temperature of the wire as a result of the electric current that passes through it is not the same in all places, because the cooling efiect of the stream of argon that is guided via tube 22 into and through guiding tube 19, differs from place to place. The cooling is the most effective on the location where the argon enters into tube 19, because there the flow has an important transverse component. Furthermore, the openings atends 20 and 21 of tube 19 are dimensioned such that the gas stream towards upper end 20 is stronger than that to lower end 21, while for both ends 20 and 21 holds that the gas stream in the narrowed end is faster and cools. stronger than in the part of tube 19 that is not narrowed.

The result is that the temperature of wire 28 shows the fastest increase approximately midway between gas supply tube 22 and end 21.

As soon as the wire has been heated to a temperature at which its strength has decreased to below the tension prevailing in the wire at that moment, it breaks. Through this the current through the wire is interrupted, so that the wire cools again.

If the temperature at which the wire breaks lies within certain limits, on either side of the breakage a torpedo-shaped point is formed.

Broken-off wire part 34, which is still held by rollers 11 and 12, is transported further by these rollers and then released. The part of the wire over the place of breakage is transported further by rollers 3 and 4 until it is caught by rollers 11 and 12 and the cycle described is repeated.

Loose wire parts 34 are the needles for the manufacture of which the described device is meant. At both ends they have a point, whose shape is determined by the temperature at which these points were formed as planes of breakage. The temperature that yields the desired torpedo-shaped points is adjusted empirically with the aid of adjustable resistor 31.

The described device was applied for manufacturing needles out of tungsten wire with a diameter of 50 p, m. The circumferential speed of rollers 3 and 4 amounted to 8.8 mm/sec., that of rollers 11 and 12 15.8 mm/sec. The-distance between the pairs of rollers was mm. The current source was adjusted to a terminal voltage of 12Vs. and was found to yield approximately 0.8 As. while the wire was heated.

Experimentally it was established that an adjustment of resistor 31 at which the charging time of the condensor amounted to approximately 0.3 sec., yielded needles with the desired torpedo-shaped points.

Both after prolonged continuous operation and after periods of stand-still of the device the pointed shape was found to be always completely reproducible.

I claim:

1. A method for manufacturing thin metal needles with at least at one end a torpedo-shaped point, wherein a continuous wire, whose thickness and material correspond with those of the needles to be manufactured and which is fed through a first driven pair of rollers, is brought again andagain with its front end between the rollers of a second pair of rollers, an increasing tensile stress is exerted on the part of the wire that hereafter is situated between the pairs of rollers by driving the second pair of rollers at a speed that is greater than that of the first pair of rollers, and then such an electric current is fed through the said part of the wire that this part of the wire is heated to a temperature at which it breaks off under the influence of the tensile stress.

2. A method according to claim 1, wherein again and again after the wire end has been fed into the second pair of rollers, a certain period of time is allowed to pass before the electric current is fed through the wire.

3. A method according to claim 2, wherein the wire is guided between the two pairs of rollers with the aid of a straight tube, which is situated with its ends near the place of outlet of the first pair of rollers and the place of inlet of the second pair of rollers.

4. A method according to claim 3, wherein a gas inert to the material of the wire is fed into the tube.

5. A method according to claim 4, wherein a stream of gas is brought into the tube-in a place between the ends and is allowed to flow away to both ends.

6. A method according to claim 5, wherein in the direction of the first pair of rollers a stronger stream of gas is fed through the tube than in the direction of the second pair of rollers.

232 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 772,495 Dated November 13, 1973 Inventor(s) Petrue- Theodorus Antonius Klaase It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Change the Assignee to read Nederlandse Organisatie voor Toegepast-Natuurwetenschappelijk Onderzoek Qen Behoeve van Nijverheid, Handel en Verkeer, The Hague, The Netherlands Signed and sealed. this 23rd (33;; of April 197A.

(SEAL) Attesc:

EDWARD I LFLETCHERJR. C. MARSHALL DANN Attesting' Officer Commissioner of Patents @2 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,772,495 Dated November 13, 1973 Inventor(s) Petrus Theodorus Antonius Klaase It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Change the Assignee to read Nederlandse Organisatie voor Toegepast-Natuurwetenschappelijk Onderzoek Een Behoeve Van Nijverheid, Handel en Verkeer, Ehe Hague, The Netherlands Signed and sealed this 23rd day of April 197A.

(SEAL) Attest:

EDWARD ILFLETCHERJR. C. 1 IARSHALL DAMN Attesting Officer Commissioner of Patents 

1. A method for manufacturing thin metal needles with at least at one end a torpedo-shaped point, wherein a continuous wire, whose thickness and material correspond with those of the needles to be manufactured and which is fed through a first driven pair of rollers, is brought again and again with its front end between the rollers of a second pair of rollers, an increasing tensile stress is exerted on the part of the wire that hereafter is situated between the pairs of rollers by driving the second pair of rollers at a speed that is greater than that of the first pair of rollers, and then such an electric current is fed through the said part of the wire that this part of the wire is heated to a temperature at which it breaks off under the influence of the tensile stress.
 2. A method according to claim 1, wherein again and again after the wire end has been fed into the second pair of rollers, a certain period of time is allowed to pass before the electric current is fed through the wire.
 3. A method according to claim 2, wherein the wire is guided between the two pairs of rollers with the aid of a straight tube, which is situated with its ends near the place of outlet of the first pair of rollers and the place of inlet of The second pair of rollers.
 4. A method according to claim 3, wherein a gas inert to the material of the wire is fed into the tube.
 5. A method according to claim 4, wherein a stream of gas is brought into the tube in a place between the ends and is allowed to flow away to both ends.
 6. A method according to claim 5, wherein in the direction of the first pair of rollers a stronger stream of gas is fed through the tube than in the direction of the second pair of rollers. 